DOUBLE WHAMMY:Landry Fields signed a three-year, $19 million offer sheet with the Raptors yesterday, and Jeremy Lin is reportedly set to sign an offer sheet with the Rockets today. Photo:

DOUBLE WHAMMY: Landry Fields signed a three-year, $19 million offer sheet with the Raptors yesterday, and Jeremy Lin is reportedly set to sign an offer sheet with the Rockets today. (AP)

DOUBLE WHAMMY: Landry Fields signed a three-year, $19 million offer sheet with the Raptors yesterday, and Jeremy Lin (inset) is reportedly set to sign an offer sheet with the Rockets today. (
)

Buddies Jeremy Lin and Landry Fields formed a backcourt 1-2 punch that became a global sensation in February.

But Tuesday, Fields and Lin provided a double-whammy of fireworks that burned Knicks general manager Glen Grunwald, with Fields signing an offer sheet with Toronto and Lin on the verge of signing one with Houston during his visit today.

The Fields’ development hurt the Knicks’ chances of executing a sign-and-trade for Steve Nash. But a source close to the situation told The Post, “It doesn’t kill it.’’

Meanwhile, Lin’s potential signing of a Rockets offer sheet will make it extremely costly to bring back Lin.

Happy Fourth of July, Glen.

Multiple sources said the Knicks will match any Lin offer sheet, but unpredictable owner James Dolan has the final say and frets about luxury-tax implications.

Toronto delivered the first blow to Grunwald when Fields, a key piece in Nash sign-and-trade talks with Phoenix, agreed to terms on a back-loaded, 3-year, $19 million offer sheet with the Raptors, according to his agent Chris Emens. The Knicks do not plan to match when it is presented to them on July 11.

Nevertheless, the source said the Knicks are working on other sign-and-trade scenarios with the Suns, with Nash’s approval. Iman Shumpert may have to replace Fields in a package that also may include Dan Gadzuric’s $1.4 million non-guaranteed contract, Toney Douglas’ expiring pact, Jerome Jordan and Josh Harrellson. Nash could end up making up to $8 million. Without a sign-and-trade, the Knicks only have their $3.09 million mini-midlevel exception.

If the Knicks lose out on Nash and match Lin’s offer sheet, they still would be in the market for a point guard with Jason Kidd, Raymond Felton, and Spanish Leaguer Pablo Prigioni very much in play. Kidd’s choices appear to be the Knicks or Dallas. The Mavericks also will turn to Nash after losing out on Deron Williams to the Nets. The Raptors could offer Nash as much as three years, $36 million, and a source close to Nash said if they do, it could be Canadian money he can’t pass up.

A league source said Lin will be offered a contract today — maybe in the $30 million range — in a back-loaded nature similar to the one the Rockets offered Bulls big man Omir Asik.

“Jeremy Lin’s an excellent player,’’ Rockets general manager Daryl Morey told The Post. “We got to know him firsthand when he was with the Rockets early this season. We think he’d make a fantastic addition to our team.’’

Lin will spend today with Morey, aiming to make up for waiving the global phenom before the regular-season opener, allowing Grunwald to pick him up on waivers.

The source said the Rockets will offer Lin $5 million, $5.2 million and then plan to jack up the third and fourth years to as much as $10 million.

Lin — who also is drawing interest from the Mavericks, according to ESPN.com — played in two preseason games with the Rockets last season, but was released before the regular season and claimed off waivers by the Knicks on Dec. 27.

“We’ll take him out to dinner and show him Houston,’’ Morey said. “He didn’t get much of a chance to see it in training camp.’’

Morey, a pioneer in basketball sabermetrics, has regretted cutting Lin.

“We should have kept [Jeremy Lin],” he tweeted in February. “Did not know he was this good. Really happy for [Lin]. … Very hard working, nice & humble. He has a great, great future.”

Grunwald has said repeatedly he will match any offer, but that offer would put the Knicks in luxury-tax hell.

Grunwald didn’t make Lin an offer at the start of free agency when he could have ended the game by offering him the maximum, four years, $23 million in the early-Bird exception. The Post reported Saturday Grunwald wanted Lin to set the market.

Had things worked out differently when free agency started, Lin would have been on a plane today to Las Vegas to get ready for the U.S. Select Team practices, but he pulled out Monday.

The Rockets’ interest makes sense because they built a giant fan base in China after drafting Yao Ming, who has since retired. Yao, who still has a relationship with the Rockets, is one of Lin’s mentors, and the Rockets free agent point guard Goran Dragic is out of the Rockets picture, according to a source.

Meanwhile, the Raptors got after Fields. According to a source, the deal has a back-loaded third year at $8.5 million. The deal cannot become official until July 11, the first day players can sign new contracts, and then the Knicks will have three days to match.

Emens said Toronto has sincere interest in Fields, but when asked if they were trying to derail a Knicks’ move for Nash he said it was “certainly plausible.”

The Knicks have talked to the Suns about a sign-and-trade with Fields as the centerpiece that would give Nash a contract starting at roughly $8 million but now go back to the drawing board.